Electrocution in a swimming pool (is it possible?)

fluppet

I didn't think Syriana was a very good film, but there was also something about it that I thought might be incorrect from a physics point-of-view: when Matt Damon's son is electrocuted in the swimming pool because there is a crack in the glass cover of one of the lights in the pool, and the water is getting in. First, it would have to be very bad wiring if the circuit wasn't tripped immediately when the water enters the light. Second, the easiest path for the current to take is going through the small bit of water between the two terminals of the light, and it wouldn't travel much further out into the pool. Third, the boy has a higher resistivity that the water, and he isn't touching anything that would make the current want to flow through him (he's surrounded by the water), so no electricity would want to flow through him anyway.
Another thing regarding this scene that I think it incorrect is that when the boy jumps into the pool, all the lights go dim for a moment, but then return to normal (presumably indicating him being electrocuted). First, if the electricity is flowing through the whole pool, the lights should be dim from the moment the glass cracks (as there is a very large load put on the circuit... a swimming pool of water would have very high resistance). Second, even if we ignore my first point about the lights being dim already, and also ignore what I said above about the electricity not going through the boy, then we are left with yet another problem of the lights returning to normal brightness after a moment... why would the large load on the circuit caused by the current passing through the boy cease once he is dead?

Am I correct in my thinking, and is this yet another inaccuracy in Syriana to add to the list?

Thomas_S_Hunterson

fluppet wrote:

Am I correct in my thinking, and is this yet another inaccuracy in Syriana to add to the list?

Yup

Michael Collins

Well people have often been electrocuted by accidentally dropping the hairdryer in the bath - it's not that hard to imagine it happening in a swimming pool. While most of the current would indeed go through the short (and hence easier) path between the two wires (assuming they were both exposed), some may leak to earth through the kid, especially since the pool would be in direct contact with the earth. Not to mention that pure water has a pretty low conductivity, much lower than that of the human body - clorine will increase this but there's no proof that the pool was clorinated. It only takes about 100 mA to cause the heart to go into fibrillation...

I'd say that - while a lot of things have to be conspiring together - it is possible. As for the lights diming - a coincidence maybe!?

All in all, probably not the most solid of points to bring up in a pub discussion of Syriana

Thomas_S_Hunterson

Michael Collins wrote:

Well people have often been electrocuted by accidentally dropping the hairdryer in the bath - it's not that hard to imagine it happening in a swimming pool. While most of the current would indeed go through the short (and hence easier) path between the two wires (assuming they were both exposed), some may leak to earth through the kid, especially since the pool would be in direct contact with the earth. Not to mention that pure water has a pretty low conductivity, much lower than that of the human body - clorine will increase this but there's no proof that the pool was clorinated. It only takes about 100 mA to cause the heart to go into fibrillation...

I'd say that - while a lot of things have to be conspiring together - it is possible. As for the lights diming - a coincidence maybe!?

All in all, probably not the most solid of points to bring up in a pub discussion of Syriana

Surely In the case of the water being relativlely pure, the distance between the boy and the electrode would likely have made any current actually reaching the boy negligible, most of the current would take the shortest path, the one of least resistance.

Then in the case that the chlorine and other salts had increased the conductivity, the electricity would take the path of least resistance to the other electrode anyway.

Michael Collins

sean_keevey wrote:

Surely In the case of the water being relativlely pure, the distance between the boy and the electrode would likely have made any current actually reaching the boy negligible, most of the current would take the shortest path, the one of least resistance.

Not if he was close enough to the wire and touching the bottom of the pool, in this case he'd be very well grounded and a small amount of current, but nonetheless a deadly amount, could pass through him. You have to think of it as a 3D problem, the current won't just take a direct line between the live wire AND the neutral wire & ground, it will be distributed through the whole pool - as a current density, lowering in magnitude as we go radially out from the live wire.

It would be unlikely enough for it to happen, but it could happen. So in the film when they say it happened, we can't really say that it's impossible.

fluppet

If he didn't touch the bottom of the swimming pool, no current would pass through him, right? When lightning strikes a lake, all the fish aren't killed (I think). Of course we don't know for sure that he didn't touch it. He just dived into the pool, but we aren't shown exactly what happens, so I suppose we have to give them the benefit of the doubt.

T.G.

Michael Collins wrote: »

Well people have often been electrocuted by accidentally dropping the hairdryer in the bath - it's not that hard to imagine it happening in a swimming pool. While most of the current would indeed go through the short (and hence easier) path between the two wires (assuming they were both exposed), some may leak to earth through the kid, especially since the pool would be in direct contact with the earth. Not to mention that pure water has a pretty low conductivity, much lower than that of the human body - clorine will increase this but there's no proof that the pool was clorinated. It only takes about 100 mA to cause the heart to go into fibrillation...

I'd say that - while a lot of things have to be conspiring together - it is possible. As for the lights diming - a coincidence maybe!?

All in all, probably not the most solid of points to bring up in a pub discussion of Syriana

That is a myth. Btw, seems that in usa electrical safety standars are non existen (judging by films and series... Including "brainy" ones... Never heard of a residual-current device or ground fault interrupter?).

Shows are shows not reality but they do tend to reflect the stupidity and ignorance of people.

dlouth15

South Fla. boy electrocuted by pool light while swimming

Quote:

"The medical examiner said Calder was electrocuted and it appears the pool light is to blame. According to an electrical contractor who inspected the equipment afterward, one of the ground wires connecting to the pool switch to the transformer wasn't attached and that sent 120 volts of electricity to the pool light, instead of the normal 12.

It appeared that strong current accelerated the corrosion of the steel that encased the light. Eventually water seeped in and turned the pool into an electrically charged body of water.

"That was a time bomb, that was a killer waiting to take somebody and the sweetest boy in the world drew the unlucky straw, which resulted in his death," Sloan said."

So it looks like an exposed ungrounded 120 volt live terminal distcharging into water is enough to kill if not wired correctly with the appropriate safety cutoffs. I think the scene in that film was set in Spain where the voltage would have been approx. 230.

Labarbapostiza

Michael Collins wrote: »

Not to mention that pure water has a pretty low conductivity, much lower than that of the human body - clorine will increase this but there's no proof that the pool was clorinated. It only takes about 100 mA to cause the heart to go into fibrillation...

If you're in water, there's essentially an electrical circuit between the fluids in your body and the water.

This is also a reason it's always a bad idea to touch any electrical appliance with wet hands.

All the current will not take the easiest path. The current is distributed proportionally to the resistance. I wonder what the formula would be for a body in a bath, if and electric heater fell in.